On 4/27/2020 3:31 PM, VanguardLH wrote:
Yousuf wrote:
I guess so far there's been no explanation of what the "AC" means yet.
My guess is that it probably stands for "Address Control" or something,
which might be a way of getting an older BIOS to understand a newer
drive. I think around this time most drives used the older CHS
(Cylinder, Head, Sector) formatting system, and to get bigger the new
generation had to switch to the newer LBA (Logical Block Address)
system. Address Control might indicate to the BIOS whether to use the
CHS system or the LBA system. Later generation BIOSes could figure this
stuff out on their own.
Even for BIOSes that supported LBA, they were and still are limited to
the number of addressing bits. At one time, 22 bits was thought
sufficient for IDE/ATA drives. Then 28 bits. Now it's up to 48 bits.
If that isn't enough for the partition size, up the entity size
(sectors). Hard disks have implemented LBA (Int13 extensions) since
1996 rather than rely on a CHS translation scheme in the BIOS.

I wasn't saying that these BIOSes couldn't understand LBA addressing,
just that they needed a manual indicator to be set, by having a jumper
switch. It would have still been early days for LBA addressing at that
point, and probably the BIOS writers couldn't be bothered to implement
self-detecting algorithms for it, so just use a jumper switch instead.

Yousuf Khan